1. Field of the Invention
This invention relates generally to information signal recording and reproducing apparatus and, more particularly, is directed to apparatus for recording and reproducing a color television signal comprised of a video signal and an audio signal on a magnetic tape with a plurality of rotary magnetic heads.
2. Description of the Prior Art
Information signal recording and reproducing apparatus for recording and reproducing a video signal on a magnetic tape by means of a rotary magnetic head assembly are well known in the art. For example, in the helical scan type video tape recorder (VTR), at least one rotary magnetic head is rotated at a predetermined angle with respect to the longitudinal or tape running direction of a magnetic tape as the latter is advanced so as to form successive video tracks extending obliquely on the magnetic tape. With the helical scan type video tape recorder, it is possible to achieve high density recording of the video signal by advancing the magnetic tape at a slow running speed and, at the same time, providing a high relative speed between the magnetic head assembly and magnetic tape. However, with known helical scan type video tape recorders in which an audio signal is recorded and reproduced on an audio track extending in the longitudinal or tape running direction of the magnetic tape by a stationary magnetic head, there results a deterioration of the signal-to-noise (S/N) ratio and an increase in the wow and flutter when the speed of advancement of the magnetic tape is reduced. This, of course, results in a deterioration in the quality of the reproduced audio signal, causing the audio signal to have unsatisfactory quality when reproduced.
In order to overcome the aforementioned problem in the recording and reproducing of an audio signal by a stationary magnetic head, it has been proposed to effect the recording and reproducing of the audio signal by means of a rotary magnetic head. With this proposal, an overscan section is provided for each oblique track, for example, by increasing the tape winding angle about the guide drum assembly of the helical scan type video tape recorder. In this manner, each record track obliquely formed on the magnetic tape by the rotary magnetic head assembly includes a video track section and an audio track section, the latter of which corresponds to the aforementioned overscan section. The audio signal that is recorded and reproduced with respect to the audio track section of each track is processed as high density data obtained by processing the signal with a time axis or base compression and a time axis or base expansion.
However, in the case described above where the audio signal is recorded and reproduced by means of a rotary magnetic head, if an external disturbance, such as a tracking error of the rotary magnetic head or drop-out of information results, there results a consequent loss of a great quantity of the reproduced audio signal which, in turn, results in large generation of noise. For example, drop-out of information may result from damage caused by a tape guide or the like to the tape edge where the audio signal is recorded at the leading or trailing end of each oblique record track. The generation of noise due to the aformentioned external disturbances is very likely where the audio signal is recorded and reproduced as a high density audio signal by means of time base compression and time base expansion processing. In such case, since the audio signal is recorded as compressed data, any tracking deviation with respect to the audio track section or any drop-out caused by damage to the tape edge will result in a large quantity of the audio signal being lost.